This invention relates to carburetors having accelerator pumps, and more particularly, to apparatus for controlling the discharge volume of the accelerator pump.
Many carburetors employ an accelerator pump for providing an additional volume of fuel to the engine when the engine is accelerated. Typically, the accelerator pump has a discharge port through which the fuel is pumped to the throat of the carburetor. In addition, a return path is provided from the accelerator pump back to the carburetor fuel bowl and the accelerator pump has a second outlet by which fuel is directed back to the fuel bowl via this return path. This second accelerator pump outlet is closed when the engine is cold so the entire volume of fuel in the accelerator pump is directed to the throat of the carburetor. This is done to improve engine drive during cold engine operating conditions. However, when the engine is hot the outlet is opened and a portion of the pump volume is directed back to the fuel bowl.
Previously, the return or bleed passage between the accelerator pump and fuel bowl has been controlled by a bi-metallic switch which closes the passage at cold engine conditions and opens the passage when the engine is sufficiently warm. This bi-metallic switch has typically comprised a snap-over disk which has a high level of operating hysterisis. This causes problems particularly when the engine cold drive condition is in the 60.degree.-80.degree. Fahrenheit range. To prevent these problems, the snap-over point for the bi-metallic disk has had to be in the range of 95.degree. Fahrenheit. However, it has been found that it takes a longer time for the disk to snap over when the disk is designed to operate at this high temperature level and as a result the engine is more responsive to air temperature than engine temperature.